Daily maintenance and adjustment method of flowmeter

Daily maintenance and adjustment method of flowmeter

Flowmeter routine maintenance items include: 1) Sealing check; 2) Zero pressure difference zero.

Sealing check includes: whether the flange fixing bolts on both sides of the differential pressure element are loose and whether there is leakage; if the pressure discharge chambers on both sides of the differential pressure are tightly tightened and leaked, whether the two ends of the cable protection sleeve are tightened or not; Or whether it is damaged, can it leak water or dust, and whether the temperature probe's protective sleeve is tightened or damaged at both ends, and whether it can leak water or dust into it; whether the front and rear covers are tightly tightened and whether it can leak water or dust; Whether the screws at both ends of the valve between the taper throttling pipe pressure holes are tightened and leaked; whether the flanges at the two ends of the pipe are well-connected, whether the screws are tightened, and whether there is leakage.

Zero pressure difference clear: close the positive and negative pressure underneath the meter head to take the needle valve on the pressure tube, and screw off the plug screw on the outfall of the pressure chamber on both sides of the differential pressure until the differential pressure in the lower right corner of the LCD is stable. Afterwards, press the “▲” and “▼” keys on the panel keys at the same time and hold them for 1 second. At the same time, release them, then press the “Save” key within 5 seconds. At this time, you will see the contents of the LCD screen switch. To display only the state of the middle row, the stored differential pressure zero value is displayed (if the value exceeds 1000, it is recommended to return to the factory for maintenance), and this state is automatically switched back to the normal measurement display interface after a few seconds. , it means that the zero point of differential pressure is cleared successfully. It is recommended that this operation be performed once every 10 days.

Flow meter measurement parameter calibration

The measurement parameters that need to be calibrated frequently at the flowmeter site include pipe pressure measurement parameters, pipe temperature measurement parameters, and throttling differential pressure measurement parameters. It is recommended that the calibration cycle be once every 15 days. The specific calibration method is as follows:

1. Calibration of pipeline pressure measurement parameters

Need tools:

1) Constant pressure output source, output pressure range: 0-250kpa;

2) 717 pressure calibrator from FLUKE, USA, measuring range: 0-300kpa;

3) American FLUKE absolute pressure calibration module, measuring range: 0-207kpa;

Calibration procedure:

2, pipe temperature measurement parameter calibration

Need tools:

1) Thermometer with accuracy higher than 0.5%, 0-100°C;

2) constant temperature water tank;

3) Ice water mixture.

Calibration procedure:

1) Enter the adjustment menu 07, 08 unit, set the temperature zero correction value of unit 07 to 0, 08 unit temperature line value is set to 1, return to the main measurement interface.

2) Put the temperature sensor head of the flowmeter into the ice-water mixture at 0°C (Note: should be placed in the constant temperature water tank), and let it stand for a period of time until the data displayed by the flowmeter temperature no longer changes. Record this time Temperature display value, and set the temperature display value to the adjustment menu 05 unit, save and exit.

3) Place the flow sensor temperature sensor head in a liquid medium with a temperature of approximately 50 °C (Note: Place in a constant temperature water tank), insert the thermometer into it, and let it stand for a while. Observe the temperature of the thermometer and record it. T0; Note the temperature display value of the flowmeter at this time, and set it as TS. Input the result of dividing T0 by TS into the menu 04, save and exit, and the temperature adjustment of the flowmeter ends.

4) Select several temperature points in the range of 0-100°C, and perform temperature test on the head temperature sensor. The error between the head temperature display value and the thermometer measurement value should be within 2.5°C. Otherwise, the calibration should be performed again.

3, the calibration of differential pressure measurement parameters

Need tools:

1) Constant pressure output source, output pressure range: 0-7kpa;

2) 717 pressure calibrator from FLUKE, USA, measuring range: 0-300kpa;

Calibration procedure:

1) Fix the meter head, close the positive and negative pressure under the meter head, take the needle valve on the pressure tube, and remove the plug screw on the sewage outlet of the pressure chamber on both sides of differential pressure, wait for the differential pressure in the lower right corner of the LCD screen. After stabilizing, press the “▲” and “▼” keys on the panel keys at the same time and hold them for 1 second. At the same time, release them, then press the “Save” key within 5 seconds. At this time, you will see the contents of the LCD screen. Switching to the state of displaying only the middle row, the stored differential pressure zero value is displayed (if the value exceeds 1000, it is recommended to return to the factory for repair), and the state is automatically switched back to the normal measurement display interface after a few seconds. Next, it represents the success of differential pressure calibration.

2) Several pressure points are arbitrarily selected within the range of 0-6 kpa, and the pressure chamber of the meter head is pressurized by a constant pressure source. The difference between the differential pressure display value measured by the meter and the measured value of the pressure calibrator should be Less than 30pa.

Note: It is recommended that the calibration period of the above parameters be calibrated once every 10 days.

General troubleshooting and solutions

The common faults on the site and solutions are as follows:

1) There is traffic in the pipe but the flow shows no traffic

Cause analysis and solution: 1, the seal is not good, there is a leak source exists; Solution: Find the source of leakage, associated with the place are: take the pressure tube valve is open, take the pressure tube valve screws are not Tightly, take a gasket in the screws at both ends of the pressure pipe valve (Note: The raw material band cannot solve the gas sealing problem!), Is the drain plug screw tightened, and whether the differential pressure element flange fixing screw is loose? Whether the two ends of the cone throttle pipe leak. 2. The flow rate of the fluid in the pipeline is too low, which exceeds the lower limit of the flowmeter measurement. Judgment method: The differential pressure measurement value is less than 0.04kpa. Solution: Replace the flow meter throttling pipe and increase the fluid velocity in the pipe. 3. A negative offset occurs in the zero point of differential pressure; Solution: Zero clear operation of differential pressure. 4, the small signal cutoff value is set too large; solution: enter the menu 35 units, set the unit value is lower. 5. The internal parameters of the flowmeter are set to the set display of the given value; Solution: Enter the menu 20/21/22/23 unit and set the value of the unit to 0. 6. The temperature and pressure measurement is not normal. Deviation from the normal value is too large, resulting in flow calculation error; Solution: Calibrate temperature and pressure.

2) The V-cone flowmeter measurement results deviate from other flowmeter measurement results in the field

Cause analysis and solution: 1, the seal is not good, there is a leak source exists; Solution: Find the source of leakage, associated with the place are: take the pressure tube valve is open, take the pressure tube valve screws are not Tightly, take a gasket in the screws at both ends of the pressure pipe valve (Note: The raw material band cannot solve the gas sealing problem!), Is the drain plug screw tightened, and whether the differential pressure element flange fixing screw is loose? Whether the two ends of the cone throttle pipe leak. 2. The relevant internal parameters are set incorrectly; Solution: Check whether the internal parameter 02 is 1. Check whether the internal parameter 06 is consistent with the factory parameter on the nameplate. Check whether the 29 unit is different from the actual density in the pipeline. . 3. Whether the flow type displayed by the current flowmeter (working flow, nominal flow, and pure gas flow) is the same as the flow type measured by the comparison flowmeter (the current display content of the V-cone flowmeter is related to the related internal parameter setting. Specific settings see the attached table). 4. Compare whether the flowmeter leaks when measuring. 5. Compare whether the flowmeter is installed and used on site correctly. 6. Compare whether the flow meter manual measurement method and measurement tool are appropriate and whether the calculation formula used is correct. 7. Whether the comparison flowmeter and the V-cone flowmeter are installed on the same pipe (Note: The two flowmeters should be installed on the same pipe so that the gas medium can pass through the two flowmeters one after another). 8. Whether the installation of the two flowmeters has reached the correct installation requirements (such as the straight pipe section requirements).

3) Inaccurate measurement of temperature and absolute pressure

Analysis of the reasons and solutions: 1, the temperature probe is not connected or the lead head and pressure line terminal contact is not good enough, re-install the temperature probe lead. 2, the temperature probe is damaged, determine the method: change the temperature probe temperature, the display value does not change. 3, the absolute pressure probe is damaged, determine the method: change the pressure corresponding to the absolute pressure chamber, observe whether the display value changes or little change. 4. Recalibrate the temperature and absolute pressure.

4) The data displayed by the frequency signal output type flowmeter at the central station is a straight line without any change

Reason analysis and solution: 1. The flow in the pipeline is relatively stable, the resolution of the substation is low, and the flow variation is lower than the minimum value that the substation can distinguish. 2. The scale of the flowmeter corresponding parameter is set too large and the frequency variation is small, which is lower than the minimum value that can be distinguished from the substation. It is recommended to replace the range of the corresponding parameter of the flowmeter or replace the substation with high resolution.

Mounting range and cone selection

When the flowmeter is in order, if the order form is filled in or the working condition parameters of the site are given, each flowmeter will make V-cone throttling pipes according to each working condition, ie different installation locations. Even if the pipe diameter is the same, the corresponding V-cone throttling pipe is different. In the field installation, the V-cone throttling pipe designed for the installation site should be selected according to the installation site.

Flowmeter on-site installation and precautions

1, the installation site selection

1 Select the position where the water in the pipeline is not easy to be obtained, and make the pipe part of the measuring pipe section higher than other pipe sections or install the automatic water ejector in its attachment;

2 Select the position away from the valve to prevent the throttling effect of the valve from affecting the measurement of the flowmeter when the valve is not fully opened. There should be a sufficiently long straight section between them, and it is better to ensure that the flowmeter has a distance of more than 5D before and after ;

3 Select the position away from the suction inlet of the pump or the position where the return water cannot reach, so as to prevent the backwater from entering the measuring tube section when the pump is stopped, and blocking the pressure-receiving hole;

4 Select the longer position of the straight pipe section. The longer the straight pipe section before and after the flowmeter, the more stable the measurement performance of the flowmeter.

(5) Selecting a position where it is not easy to achieve large solid impurities or adopting certain measures to make solid particles difficult to reach the flow meter to measure the pipe section

6 Select the lightning protection grounding position to facilitate the lightning protection grounding treatment of the flowmeter.

2, flow meter installation steps

1 Install the flowmeter throttling pipe to the pipeline to be measured, where the differential pressure element is marked with "H" side pressure pipe connected to the throttling element to the gas direction pressure pipe, "L" followed by another Pressurize the tube and check the airtightness. The positive pressure pipeline can be inspected by applying soapy water to the joints. Where there is leakage, soap bubbles will rise. The negative pressure pipeline can be placed on tiny paper strips or strips. Near the interface, to see if there is adsorption to check the airtightness;

2 Install the meter head on the two pressure tubes. There should be a needle-shaped stop valve on the pressure tube. There should be a white gasket at each joint of the stop valve. Then check the airtightness, with the method â‘ ;

3 Insert the temperature sensor head into the pipe temperature measurement hole and insert it into the bottom. Then connect the temperature sensor head lead through the high pressure pipe to the corresponding position of the flowmeter meter head. It does not divide the positive and negative poles, two lines of the same color The stripped shells are screwed together. The other color wire is also stripped of the shell and pressed against the terminal post. Note: Since the temperature lead is thin, it is recommended to be able to strip the wire when the wire is not easily broken. A section of the shell is also pressed under the pressure line to enhance the toughness of the lead;

4 Enter the flow coefficient, and input the data of C3 on the throttle plate to the internal parameter 6 of the meter;

5 Input small signal cutoff value, different diameters of small signal cutoff are not the same, the minimum value of C4 on the nameplate of the throttle is multiplied by the cross-sectional area of ​​the pipe and then multiplied by 3600. The result is input to the internal parameter 35;

6 flow adjustment, enter the internal parameter 02 unit, the unit default is 1, changing the data will change the corresponding flow multiple;

7 Adjust the zero point of differential pressure, turn off the valve, open the drain plug, press the up and down keys at the same time, and then press the save button, then the liquid crystal display no longer refreshes, this situation lasts about 2s, the header Reset, wait about 30s, the differential pressure display tends to be stable, the differential pressure should be displayed as 0, then the differential pressure zero clearing is successful;

8 Set the unit's address number, enter the menu 1 unit, set the machine's address number, the address number can be set from 1-128.

Key use and parameter modification method

1, the use of keys:

“Function” key: Function setting selection key, press this key to display the function number of the internal parameter displayed on the low level of the accumulated flow. Press 1 time to display a set of parameters. Press this key repeatedly to cycle through 40 groups of parameters for 01-40.

“△”: parameter modification key (digital increase key), press 1 time to modify the number of flashing display, and return to complex number will flash display number from 0 0. 1 1. 2 2. ......9 9 Cycle modification. Each bit of data is divided into two types, with or without a decimal point.

“▽”: Parameter modification key (digital decrease key), press 1 time to modify the number of flashing display, and return to complex number will flash display number from 9 9. 8 8. 7 7. ...0 0. Loop modification. Each bit of data is divided into two types, with or without a decimal point.

"?": Right shift key, repeatedly press this key, the set value digit moves to the right.

“ ? ”: Left shift key, press this key repeatedly, the set value digit moves to the left.

“Save”: Confirmation key, press this key, the set parameter value is valid.

“RESET”: At the top right of the motherboard, pressing this key will force reset the instrument.

2, modify the parameter method

1) Press the "function" key to enter the menu, press the "function" button again, switch the function number;

2) The flashing value is the data bit that can be modified at present, press "â–³" "â–½" to modify the data bit, press "?" " ? " to move the data bit to be modified;

3) Press the "Save" button. If it is saved successfully, an "A" will appear in the lower left corner of the LCD, and then it will disappear and the data will be saved successfully.

4) Press the "function" button continuously, the instrument will automatically exit the menu interface and switch to the main measurement interface after all the function numbers have circulated; if you press the "RESET" button on the main board under the menu interface, the instrument Will reset.

Flow meter header commonly used function configuration table is as follows:

Display type

Function number

Display discrimination

Unit 16

Unit 17

Unit 19

Condition mixed flow display

Hours

1

0

There is “m 3 /h” at the end of the middle row of the liquid crystal, and the cumulative unit of the first row of the liquid crystal shows “m3” and “Nm3”. The cumulative amount at this time is the amount of mixed amount

Minutes

1

1

There is no unit display at the end of the middle row of the liquid crystal, and the first row cumulation unit of the liquid crystal shows “m3” and “Nm3”. The cumulative amount at this time is the amount of mixed amount

Standard mixed flow display

Hours

0

0

There is “Nm3/h” at the end of the middle row of the liquid crystal, and the first row cumulation unit of the liquid crystal shows “Nm3”. At this time, the cumulative amount is the amount of mixed amount

Minutes

0

1

There is no unit display at the end of the middle row of the liquid crystal, and the first row cumulation unit of the liquid crystal shows “Nm3”. The cumulative amount at this time is the amount of mixed amount

Pure flow display

Hours

2

0

There is “Nm3/h” at the end of the middle row of the liquid crystal. The cumulative amount of the first row of the liquid crystal shows no unit. The cumulative amount at this time is the cumulant amount.

Minutes

2

1

There is no unit display at the end of the middle row of the liquid crystal, and the first row of liquid crystals has no unit display. The cumulative amount at this time is a cumulant

temperature display

0

There is "°C" in the lower left corner of the LCD

Differential pressure display

1

There is no unit display in the lower left corner of the LCD. The actual unit is kpa.

Temperature, differential pressure display

2

There will be a "°C" in the lower left corner of the LCD, and it will disappear. When the "°C" is displayed, the front figure represents the temperature. When there is no unit display, the front figure represents the differential pressure, and the actual unit is kpa.

Coal mine commonly used orifice calculation formula (for D-1/2D pressure way orifice plate)

Where: k is the orifice plate coefficient, and it is determined whether the calculated flow is a minute amount, an hour amount, or a second amount according to the difference of the information of the orifice plate coefficient. Note that k contains the information of the acceleration of gravity. Please check if the coefficient contains information in use. If it is, the result calculated by this formula should be multiplied by the square of 9.8. The t working unit is °C, the p working unit is mmHg, the hmmh20 unit is mm water column, and C is the gas concentration, and the unit is %.

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